WO2015197635A1

WO2015197635A1 - Multi-thread tandem cells

Info

Publication number: WO2015197635A1
Application number: PCT/EP2015/064141
Authority: WO
Inventors: Tristan LESCOUET; Solenn Berson; Caroline Celle; Pierre-Balthazar LECHENE; Jean-Pierre Simonato
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives; Universite De Chambery - Universite Savoie Mont Blanc
Priority date: 2014-06-26
Filing date: 2015-06-23
Publication date: 2015-12-30
Also published as: KR20170048323A; EP3161883B1; US20170207405A1; JP2017522729A; EP3161883A1; FR3023067B1; JP6718384B2; FR3023067A1

Abstract

The present invention relates to a multi-layer stack which is useful for forming a multi-junction organic photovoltaic cell, said stack including first and second active layers, and an intermediate p-type or n-type layer, inserted between said first and second active layers and in contact with at least one of the first and second active layers, said intermediate layer including a network of electrically conductive nanowires, said stack including an additional layer, inserted between the first active layer and the second active layer and directly in contact with the first active layer or the second active layer, the additional layer being P-type or N-type, separate from the one forming the intermediate layer.

Description

MULTIFILES TANDEM CELLS

The present invention relates to the field of organic photovoltaic cells. The so-called organic photovoltaic cells generally comprise a multilayer stack comprising a photoactive layer, called the "active" layer. This active layer is called "I" and is generally composed of one or more intrinsic semiconductor materials or of a mixture of P type and N type materials. These semiconductor materials are generally organic molecules. or halogenated polymers or organometallic compounds. This active layer is in contact on both sides with an N-type layer and a P-type layer. The P-type layer is generally composed of a mixture of poly (3,4-ethylenedioxythiophene) (PEDOT) and sodium poly (styrene sulfonate) (PSS), or a P-type semiconductor oxide, for example WO ₃ , Mo (¾, V ₂ O _5, or NiO) .The N-type layer generally consists of an oxide semiconductor of n-type, for example ZnO, AZO (zinc oxide doped with aluminum) or TiO _x. This type of multilayer structure composed of the superposition of the active layer I and the two layers of type P and type N described above is conventionally referred to as N3P or PIN.

The electrical efficiency of an organic photovoltaic cell is particularly dependent on the absorption spectrum of light of the active layer.

To improve this yield, organic photovoltaic cells of the multi-purpose type, and in particular of the "tandem" or double-junction type, are developed. Such tandem type cells comprise two PIN and / or NIP multilayer assemblies as described above, stacked one on top of the other, and whose respective active layers generally have different absorption spectrums of light. It should be noted that in the case of organic photovoltaic cells of the tandem type, the multilayer NIP or PIN assembly is generally designated as a simple junction. In these tandem type cells, the photons that are not absorbed by the first active layer can be absorbed by the second. The quantity of photons recovered by all the active layers of the cell is thus increased and the electrical efficiency of the latter is improved.

As an illustration of the organic photovoltaic cells of the tandem type, mention may be made especially of the so-called "2-wire" and "3-wire" cells. In a 2-wire type cell, the multilayer stack defines an electrical assembly in series. The upper layer of the lower multilayer assembly, of the N or P type, forms with the lower layer of the upper multilayer assembly, respectively of the P or N type, a multilayer element for recombining the charge carriers (electrons and holes), whose thickness is generally between 40 nm and 200 nm. To recombine the charge carriers more efficiently, it may be interposed a metal layer and semi-transparent, in particular silver, which substantially completely covers the interface between the two layers constituting said multilayer element recombination.

Nevertheless, the intensity J of the current in a 2-wire cell remains limited by the least efficient multilayer assembly.

The so-called "3-wire" cells make it possible to overcome this handicap.

Thus, the "3-wire" cell described in the article "High-efficiency polymer tandem solar cells with three terminal structure", Srivinas Sista et al, Adv. Mater., 2010, 22, E77-E80, consists of an assembly consisting of a multilayer assembly NIP superimposed on a multilayer assembly ΡΓΝ, first and second electrodes arranged on either side and in contact with each multilayer assembly. ΝΓΡ or ΡΓΝ, and a central electrode, formed of a gold layer, disposed at the interface between the two multilayer assemblies ΝΓΡ and PIN. In such an assembly, the lower and upper electrodes are in contact and are connected to the central electrode, so as to form a parallel connection of the PIN and NIP multilayer assemblies. Thus, the total current J in this type of photovoltaic cell does not appear to be affected by a potential current difference between the two multilayer assemblies PIN and ΝΓΡ, respectively.

As previously described, a tandem type assembly mentioned above also incorporates a metal layer. However, the implementation of this metal layer imposes certain constraints.

Thus, the metal layer at the interface between the multilayer PIN and / or ΝΓΡ assemblies of the assembly must not be too thick to guarantee a high transmittance so that the photons can, after passing through the first active layer and the metal layer, reach the second active layer. However, it is known, as attested by the article "Highly efficient organic tandem solar cells: afollow up review", Ameri Tabeyeh et al, that a reduction in the thickness of this metal layer can cause conduction problems, harmful to the performance of the photovoltaic cell. Finally, as opposed to the active layers, type N and type P classically deposited wet, the deposition of this metal layer requires a vacuum evaporation technique. In industrial terms, this technique proves expensive and not easy to implement.

Alternatives to metal electrodes are already known. They take advantage of other conductive materials such as polymer mixtures, for example PEDOT and PSS, metal-polymer composites, metal grids, metal nanowires, carbon nanotubes, graphene, and metal oxides. . In the article "Flexible ITO-Free Polymer Solar Cells", Dechan Angmo, Frecerik C. Krebs, J. Appl. Polym. Sri., vol. 129, num. 1, 1-14, 2013, DOI: 10.1002 / app.38854., It is in particular proposed the implementation as transparent top electrode of a network of silver nanowires. However, the high roughness of the nanowire network can lead to the creation of short circuits. In addition, the empty areas between the silver nanowires limit the ability to extract charges between the adjacent N or P layer and the electrode. Finally, the output work of the silver nanowires network is not suitable for extracting the charges.

Consequently, there remains a need for a multi-layer stack for a multi-function organic cell, in particular of tandem, 2-wire or more type, the development of which is at least partially free of the problems described above.

The present invention is precisely to meet this expectation.

Thus, according to a first of its aspects, the present invention relates to a multilayer stack useful for forming an organic photovoltaic cell of the multijunction type, in particular of the tandem type, said stack comprising first and second active layers, and an intermediate layer of the type P or N type, interposed between said first and second active layers and in contact with at least one of the first and second layers, characterized in that said intermediate layer includes a network of electrically conductive nanowires.

Against all expectations, the inventors have indeed found that a stack according to the invention proves particularly advantageous for forming a multi-function photovoltaic cell, in particular of the tandem type.

First, it provides access to an advantageous compromise in terms of surface resistivity and transmittance. Moreover, the network of nanowires may have a thickness greater than that of a metal layer, but less than that of the layer that it incorporates. The conductive network thus formed allows efficient recombination or extraction of the charge carriers with a small decrease in the transmittance of the stack with respect to a stack without the nanowire array.

Thus, an organic photovoltaic cell of the multi-function type, and in particular of the tandem type, comprising a stack according to the invention has improved energy efficiency compared to organic photovoltaic cells of the multijunction type, and in particular of the tandem type, of the prior art.

The invention also relates to a method of manufacturing a multilayer stack according to the invention, comprising at least the steps of:

a) having a first active layer in contact with a first type P or type N coating,

b) depositing on said first coating a first solution comprising nanowires and optionally a P type or N type material, under conditions conducive to the formation, on the surface of said first coating, of a second coating incorporating a network of nanowires,

c) optionally, depositing on the second coating formed in step b) a second solution comprising a P-type or N-type material, identical to or different from that of the first solution, under conditions conducive to the formation of a third coating.

The method according to the invention is simpler to implement and less expensive than the processes for manufacturing stacks comprising a vacuum evaporation step of a metal layer of the prior art. In particular, all of the coating deposition steps for forming the multilayer stack according to the invention can be carried out wet. In addition, all the deposition steps of the different layers of the stack can thus be performed with the same deposition device.

The invention also relates to a photovoltaic cell of the multijunction type, and in particular of the tandem type, comprising a multilayer stack according to the invention or obtained by means of a method according to the invention. Advantageously, the recombination multilayer element may be thicker than in a prior art 2-wire tandem type organic photovoltaic cell, while having a substantially identical transmittance. It is thus possible to modulate the optical field of the multilayer recombination element to increase the amount of photons collected by the active layers, and without losing the surface resistivity or mobility of the charge carriers.

The invention can be better understood on reading the following detailed description and on examining the appended drawing, in which:

FIGS. 1 and 2 illustrate stacks of organic photovoltaic cells of tandem 3-wire type according to the invention,

FIGS. 3 and 4 illustrate stacks of organic photovoltaic cells of tandem 2-wire type according to the invention,

FIGS. 5 and 6 illustrate an intermediate layer incorporating a network of nanowires of a stack according to the invention, in side view and in plan view respectively, and

FIGS. 7 and 8 illustrate steps of the method of manufacturing a stack according to different modes of implementation.

In the different figures, identical or similar members have been identified with the same reference. In the appended drawing, the actual proportions of the various constituent elements of the stack have not always been respected for the sake of clarity.

STACK

As illustrated for example in FIG. 1, a stack 5 according to the invention may notably comprise a succession of layers superimposed and joined to each other in the following order:

a first outer layer 14,

a first active layer 17,

an intermediate layer 20 which integrates a network 22 of nanowires,

a second active layer 23, and

a second outer layer 26, As will be seen later, in a particular embodiment, the stack may further comprise an additional layer disposed between the first active layer or the second active on the one hand and the intermediate layer on the other.

In a first embodiment of the invention, the multilayer stack is more particularly intended to be used to form a 3-wire tandem type organic photovoltaic cell. In this case, the intermediate layer is directly in contact with the first and second active layers. In other words, the stack then has no additional layer.

More particularly, as illustrated in FIG. 1, the stack according to the first embodiment forms a multilayer assembly of PESIIP 35 type, consisting of a first P type outer layer, a first active layer, a layer N-type intermediate, a second active layer and a second P-type outer layer.

As a variant, as illustrated in FIG. 2, the stack forms a NIPIN 38 multilayer assembly consisting of the first N-type outer layer, the first active layer, the P-type intermediate layer, and the second layer. active and the second N-type outer layer.

As illustrated in FIGS. 1 and 2, the network 22 of nanowires of the stack according to the first embodiment of the invention is preferably disposed substantially at mid-distance from the interface between the first active layer and the intermediate layer on the one hand, and the interface between the second active layer and the intermediate layer on the other. Π is intended to form the central electrode of the tandem type 3-wire organic photovoltaic cell. Preferably, in this variant, the nanowires that constitute the network are metallic, and in particular comprise or consist of a metal chosen from silver, gold, copper or their alloys. Money is a favorite metal.

In a second embodiment of the invention illustrated in FIGS. 3 and 4, the multilayer stack is more particularly intended to be used to form a 2-wire tandem type organic photovoltaic cell. In this case, the stack comprises an additional layer 41, interposed between the first active layer and the second active layer and directly in contact with the first active layer or the second active layer, the additional layer being of a P or N type, distinct from that forming the intermediate layer 20.

Preferably, the additional layer is interposed between the intermediate layer on the one hand and the first active layer or the second active layer on the other hand, and is in contact with the intermediate layer on the one hand and the first active layer or second active layer on the other hand.

More particularly, a stack according to the second embodiment can form a PINPIN-type multilayer assembly 44 consisting of a first PIN-type multilayer assembly 47 comprising a first P-type outer layer, a first active layer, an intermediate layer of the type N or an additional N-type layer, and a second PIN-type assembly 50 comprising an additional P-type layer or a P-type intermediate layer, a second active layer and a second N-type outer layer. Such an example PINPIN type stacking device is illustrated in FIG.

As a variant, as illustrated in FIG. 4, a stack according to the second embodiment can form a NIPNIP 53 multilayer assembly consisting of a first NIP-type multilayer assembly 56 comprising a first N-type outer layer, a first layer active, a P-type intermediate layer or an additional P-type layer, and a second multic-type multilayer assembly 59 having an N-type additional layer or an N-type intermediate layer, a second active layer and a second layer. external type P.

According to the second embodiment of the invention, as illustrated in FIGS. 3 and 4, the network 22 of nanowires is preferably at least partially in contact with the additional layer, and preferably extends to the interface between the intermediate layer and the additional layer. Thus, the assembly formed by the intermediate layer integrating the nanowire array and the additional layer forms a multilayer charge recombination element for the 2-wire tandem organic photovoltaic cell.

NANOWIL NETWORK

The nanowire network of the stack is formed of an irregular and disordered assembly of nanowires. In particular, the network of nanowires has no distance characteristic according to which an elementary and characteristic pattern of the network is reproduced. Thus, a network is different from a grid.

Preferably, the network 22 of nanowires extends parallel to the intermediate layer 20. Preferably, less than 5%, less than 1%, or substantially none of the nanowires of the nanowire network is in contact with the first active layer and / or the second active layer. In a preferred manner, the network of nanowires is devoid of contact with said first and second active layers.

As schematically illustrated in FIG. 5, the network 22 of nanowires preferably extends along a substantially planar surface S _p , called the grating plane below, preferably parallel to the interface between the intermediate layer. 20 and the layer immediately above and / or immediately below and in contact with the intermediate layer.

Preferably, the nanowires forming the nanowire network can be distributed isotropically within this network as can be seen in FIG. 6.

Preferably, the distribution of the nanowires within the nanowire array is homogeneous.

Preferably, the nanowire density of the network, expressed as an equivalent weight of silver per unit area, is between 0.01 gm ² and 0.05 g / m ² . By quantity of nanowires expressed as the equivalent mass of silver constituting the nanowires, the total mass of the volume of the considered nanowires which would be made of silver, whatever the material constituting the nanowires, is considered.

Preferably, the thickness e _p of the nanowire array is less than 300 nm, preferably less than or equal to 200 nrn, and is more particularly between 40 nm and 200 nm.

Preferably, the intermediate layer, observed in a vertical direction, is such that the surface fraction occupied by the nanowire network represents less than

80%, less than 50%, less than 30%, or even less than 10%.

In the case of a 3-wire tandem organic photovoltaic cell, the nanowires of the nanowire network 22 have points of contact with distinct nanowires of the nanowire network. This is called percolation between the nanowires, which allows the network

22 to play the role of central electrode for the photovoltaic cell. The network of nanowires can also be percolating when the stack which comprises it is intended for a 2-wire type tandem photo voltaic cell.

In particular, in the case of a tandem organic photovoltaic cell of the 2-wire type, the nanofilm network 22 does not necessarily need to be percolating since the assembly formed with the intermediate layer and the additional layer is intended to form a multilayer charge carrier recombination element.

Thus, in one embodiment, in particular, the nanowire network is non-percolating, that is to say that the nanowires are free of contact with each other.

The ability of the nanowire array to extract charges from the adjacent layer can be evaluated by measuring its output work. In the case where the nanowire network consists of silver nanofilts and / or copper nanofilts, the output work of the nanowire network is preferably between 4.7 eV and 5.2 eV.

Preferably, the nanofilts which constitute the network are metallic, and in particular comprise or consist of a metal chosen from silver, gold, copper or their alloys. Money is a favorite metal.

Preferably, the nanowires have a mean diameter greater than 10 nm, preferably greater than 20 nm, and less than 1000 nm, preferably less than 150 nm. Preferably, they have an average length greater than or equal to 1 μιη and less than or equal to 500 μπι, preferably less than or equal to 30 μτη. In particular, the average slenderness ratio of the nanowires is preferably greater than 100.

The diameter of a nanowire may be between 10 nm and 1000 nm. The length of a nanowire can be between 1 μηι and 100 μηι, preferably between 5 μτη and 20 μηχ

Preferably, more than 70%, more than 90%, or substantially all nanofilts have an aspect ratio of greater than 100.

INTERMEDIATE LAYER

The nanowire network is integrated in an intermediate layer which advantageously has at least one of the characteristics described above.

It is formed at least in part, or completely of a P type or N type material. A type of material allows the transport of electrons. A material of type P allows the transport of the holes. A P-type or N-type material may be a conductive or semiconductive oxide, or a conductive or semiconductive polymer.

The P type material may be, for example, chosen from poly (3,4-ethylenedioxythiophene) (PEDOT): sodium poly (styrene sulfonate) (PSS), Nafion, WO ₃ , M0O ₃ , V 2 O 5 and O, and mixtures thereof. .

A preferred type P material is the mixture of PEDOT and PSS.

An N type material may for example be chosen from ethoxylated polyethylenimine (PEEE), poly [(9,9-bis (3 ^, - (N, N-dimethylamino) propyl) -2,7-fuorene). 2,7- (9,9-dioctylfluorene) (PFN), ZnO, titanium oxides TiO _x with x between 1 and 2, zinc oxide doped with aluminum (AZO), zinc oxide doped with Pindium (IZO), gallium doped zinc oxide (GZO), and mixtures thereof.

Preferred N-type materials are ZnO and TiO _x .

In the case where the intermediate layer comprises an N-type material, the output work of the nanowire array is preferably between 4.0 eV [electron-volt] and 4.8 eV. In the case where the intermediate layer comprises a P-type material, the output work of the nanowire network is preferably between 4.8 eV and 5.3 eV.

According to the first embodiment of the invention, preferably, the thickness of the intermediate layer is greater than or equal to 100 nm and less than or equal to 500 nm. It can be measured with an AFM atomic force microscope with the VEECO / IKNOVA trade name or with a KLA Tencor profilometer.

Preferably, according to the first embodiment, the transmittance of the intermediate layer is greater than 50% and / or the surface resistivity of the intermediate layer is less than 200 Ω / sq, preferably less than 100 Ω / sq.

According to the second embodiment of the invention, preferably, the thickness of the intermediate layer is greater than or equal to 100 nm and less than or equal to 500 nm.

OTHER LAYERS OF THE STACK

As previously described, according to the second embodiment, the stack comprises an additional layer of a P-type or N-type material distinct from that of the intermediate layer, in particular a P- or N-type polymer and / or an oxide of type P or N respectively, as described above. li

Preferably, the intermediate layer is then made of ZnO and the additional layer is then in a mixture of PEDOT and PSS.

Alternatively, the intermediate layer is a mixture of PEDOT and PSS and the additional layer is ZnO.

The additional layer preferably has a thickness between 50 nm and 300 nm.

The assembly constituted by the intermediate layer and the additional layer preferably has a thickness greater than or equal to 1000 nm and less than or equal to 500 nm. Preferably, the transmittance of the assembly constituted by the intermediate layer and the additional layer is greater than 50% and / or the surface resistivity of the assembly constituted by the intermediate layer and the additional layer is less than 200 Ω / sq, preferably less than 100 U / sq.

According to the embodiment, the stack also comprises first and second active layers disposed on either side of the intermediate layer, and optionally the additional layer.

The first active layer may be of a material mixture different from that of the second active layer, so as to have a spectrum of light absorption different from the spectrum of the second active layer.

It can also be formed of the same mixture of materials.

The choice of materials and the thicknesses of the first and second active layers can be done conventionally in the field of multi-function organic photovoltaic cells. The materials chosen are in particular organic molecules and / or polymers. According to one variant, the material or materials of the active layers could also be chosen from halogenated organometallic compounds such as CH ₃ NH ₃ Pbl 2, the lead may be replaced by tin or germanium and the iodine may be replaced by chlorine or chlorine. bromine. Such a photovoltaic cell can in this case be designated as a photovoltaic cell in perovksite, because of the material constituting the active layer or layers, the architecture of such a cell remaining no less identical to that of a cell. organic photovoltaic multijunction. Thus, in the context of the present invention, it is possible to assimilate such a photovoltaic cell in perovskite to a multi-function organic photovoltaic cell. As an illustration, a stack according to the first embodiment of the invention may comprise:

a first active layer consisting of a mixture of P3HT and PCBM; an intermediate layer which integrates a network of silver nanowires and consisting of ZnO; and

a second active layer consisting of a mixture of P3HT and PCBM.

In a preferred variant, a stack according to the first embodiment of the invention may comprise:

a first active layer consisting of a mixture of P3HT and PCBM,

an intermediate layer that integrates a network of silver nanowires and consists of a mixture of PEDOT and PSS, and

a second active layer consisting of a mixture of P3HT and PCBM. For its part, a stack according to the second embodiment of the invention may comprise;

a first active layer consisting of a mixture of P3HT and PCBM,

an additional layer consisting of a mixture of PEDOT and PSS,

an intermediate layer which integrates a network of silver nanowires and consists of ZnO,

a second active layer consisting of a mixture of P3HT and PCBM.

In a preferred variant, a stack according to the second embodiment of the invention, comprising a P-type intermediate layer and an N-type additional layer may comprise:

a first active layer consisting of a mixture of P3HT and PCBM,

an additional layer consisting of ZnO,

an intermediate layer which integrates a network of silver nanowires and consists of a mixture of PEDOT and PSS,

a second active layer consisting of a mixture of P3HT and PCBM. In particular, as illustrated in FIGS. 1 to 4, the stack may also comprise first and second outer layers.

Preferably, the first and second outer layers are made of an N- or P-type material, preferably selected from the N- and P-type polymers and / or oxides as described above to form the intermediate layer. The constituent materials of the first and second outer layers may be different. Alternatively, they are identical.

The thickness of the first outer layer and / or the second outer layer may be greater than 20 nm, or even greater than 50 nm and / or less than 250 nm, or even less than 200 nm, or even less than 100 nm.

MANUFACTURING PROCESS

The method of manufacturing a stack according to the invention is such that all of the deposition steps for forming the stack according to the invention can be carried out by wet process, that is to say by a technique using the deposit of a liquid solution.

In particular, the deposition of a solution during the manufacturing process can be carried out by means of a technique chosen from spin coating, scraping, ultrasonic spray deposition, spin coating. slot, inkjet printing, rotogravure, flexography or screen printing. In particular, all the coatings deposited during the process steps can be deposited using a single technique chosen from those described above. In particular, the deposition technique may also be chosen by those skilled in the art depending on the fluid properties and the constituents of the solution to be deposited. A layer can be obtained by at least one or more deposition steps.

Preferably, a solution deposited during the implementation of the process comprises a solvent. The solvent may be water and / or dimethyl sulfoxide and / or an alcohol, for example selected from isopropanol, ethanol, methanol, glycerol, ethylene glycerol, or mixtures thereof.

The characteristics specific to the different steps of the process are described below. Step a) uses a multilayer structure 60 formed at least in part of a first active layer in contact with a first type P or type N coating.

As illustrated in FIG. 7, the multilayer structure 60 may advantageously be represented by a support 8 on which is arranged a succession of layers superimposed on each other.

In a preferred embodiment, it may comprise:

a support 8,

a first electrode 1 1,

a first outer layer 14,

a first active layer 17,

a first coating 63,

In particular, the first outer layer and the first coating may consist of type N or type P materials described above. The constituent layers of the multilayer structure 60 considered in step a) can be obtained by wet process.

Thus, the first coating can be previously formed by depositing on the outer surface of the first active layer a solution under conditions conducive to its formation. This solution may comprise an N or P type material, in particular a polymer and / or a P type oxide, dissolved in a solvent, in particular as described above, and may also comprise a surfactant and / or a surfactant. viscosity as described above.

Preferably, this first coating has a thickness of between 20 nm and 100 nm. The method implements in step b) a deposition on the first coating of a first solution comprising nanofilaments and optionally a P-type or N-type material, under conditions conducive to the formation on the surface of said first coating. , a second coating incorporating a nanofiis network.

Step b) can result in the formation of first and second structurally different coatings, depending on whether it is implemented in a first mode or a second mode as described below. In a first embodiment of step b), illustrated in FIG. 7, the first solution may then consist of a dispersion of nanofilms in a solvent as described previously. The concentration of nanofilaments, expressed as equivalent silver mass constituting the nanofilies per liter of first solution, is then preferably between 0.1 g / l and 10 g / l.

The first solution may be deposited on the first coating so as to form a network of nanowires by means of a deposition method as described above, and in particular by slit die coating, or by gravure printing, or by jet printing. ink, or preferably by ultrasonic spray. Those skilled in the art know how to adapt the deposition parameters to deposit a sufficient quantity of nanowires so as to form a conducting nanowire network after removal of the solvent from the first solution.

Preferably, this first embodiment results, at the end of step b), in the formation of a second coating 64 constituted by the network 22 nanofiîs.

Preferably, the deposition parameters of the first solution are adapted so that at the end of step b), the transmittance of the nanowire network is greater than 70% and the surface resistivity of the nanowire network is less than 50 Ω / sq, and / or the surface density of the nanofilm network, expressed as the equivalent weight of silver constituting the nanofilies per unit area, is between 0.005 g / m ² and 0.1 g / m ² , more particularly between 0.01 g / m ² and 0.05 g / m ² .

In a second embodiment of step b), illustrated in FIG. 8, the first solution deposited in step b) comprises a type P or type N material, as described previously. In particular, the first solution in step b) can then be obtained by mixing first and second liquid preparations.

The P or N type of the material of the first solution deposited in step b) may be identical or different from the P or N type of the material of the first coating.

The first liquid preparation may consist of a dispersion of nanofilas in a solvent as described above in a concentration greater than or equal to 0.1 g / l, preferably greater than or equal to 0.5 g / l, and less than or equal to 10 g / l, preferably less than or equal to 5 g 1. The second liquid preparation may, for its part, have a mass content of P type material or N type between 1% and 40%. To form the second liquid preparation, a P-type or N-type polymer is preferably dissolved in water. Alternatively, a P-type or N-type metal oxide may be dissolved in water and / or an alcohol as described above. The second liquid preparation may further comprise a viscosity agent and / or a surfactant to modify the viscosity and / or surface tension of the first solution.

The first solution, consisting of the first and second liquid preparations is preferably deposited by spinneret, or scraper, or by ultrasonic spray, or by slit die coating, or by inkjet printing.

In this second embodiment, the deposition parameters of the first solution are preferably adapted so that at the end of step b), the transmittance of the succession of the first coating 63, nanowire network and second coating 64 is greater than 50% and the surface resistivity of the succession of the network of nanowires and the second coating is less than 100 Ω / sq, and / or the surface density of the network of silver nanowires, expressed in equivalent weight of silver constituting the nanowires per unit area, is between 0.01 gm ² and 0.05 g / m ² .

Alternatively, the method according to the invention may further comprise a step b ') carried out after step b) and before step c), of depositing a solution comprising nanowires on the first coating formed in the step b) under conditions conducive to the formation of a coating superimposed on the first coating and on which the second coating is subsequently deposited. This solution then preferably comprises a material of the same N or P type as the first solution, so that the first coating and the coating formed in step b ') define a homogeneous intermediate layer incorporating a network of nanowires having a specific gravity. variable nanowires depending on the thickness of the layer. Such a step b ') can in particular be implemented for the manufacture of a useful stack for a 3-wire type photovoltaic cell.

The method according to the invention also optionally implements a step c) which consists in depositing on the second coating formed in step b) a second solution comprising a type P or N type material, identical to or different from that of the first solution, under conditions conducive to the formation of a third coating (66).

Step c) is in particular implemented when in step b), the first solution consists of a dispersion of nanowires in a solvent according to the first embodiment of the method as described above. Preferably, the second solution is then deposited directly on the network of nanowires formed in step b).

The second solution preferably comprises a material of P or N type in a solvent as described above. The second solution implemented in step c) may in particular be identical to that implemented in step a).

Preferably, the amount of second solution deposited in step c) is adapted so that after removal of the solvent, the thickness of the third coating 66 is greater than the thickness of the network of nanowires formed at the end of the step b). Preferably, the thickness of the third coating is between 50 nm and 400 nm.

Preferably, at the end of step c), the third coating integrates at least partially, preferably completely, the second coating, in particular constituted by the network of nanowires formed in step b).

In this way, the nanowire array forms an electrically conductive structure within a matrix comprising a P-type or N-type material and constituted at least in part by the third coating.

Preferably, the deposition parameters of the second solution are preferably adapted so that at the end of step c), the transmittance of the assembly consisting of the first 63, second 64 and third 66 coatings is preferably greater than 50% and the surface resistivity of the third coating 66 is preferably less than 100 Ω / sq.

The coatings formed in steps a), b) and, where appropriate, c) form, depending on the manner in which the process is carried out and according to the choice of the N or P type of the materials constituting the coatings, a single intermediate layer or a layer. intermediate and an additional layer of the stack.

In particular, the first coating may constitute the additional layer 41 on the one hand, and the second coating, and optionally the third coating, may constitute the intermediate layer 20 on the other hand.

Alternatively, as illustrated for example in Figure 7, the first 63, second 64, and optionally third 66 coatings constitute the intermediate layer 20. In other words, the choice of the N or P type of the material constituting each of the coatings of steps a), b) and c) makes it possible to form at the end of step b) or, if appropriate, of step c) an electrode central unit 70 or a multilayer charge carrier recombination element 45 of a photovoltaic cell comprising a stack according to the invention, as will be described below.

In particular, when in step a), the first coating comprises an N-type or P-type material, and in step b) and / or step c), the second and / or or the third coating comprises (nt) an N-type or P-type material, the assembly of the first, second and, if appropriate, third coatings constitutes the intermediate layer, integrating a network of N-type or P-type nanowires, respectively. of the stack according to the invention.

Alternatively, when in step a), the first coating comprises a material of type P, respectively of type N, and that in step b) and / or in step c), the second and / or 3rd third coating comprises (nt) a N type material, respectively P type, the first coating may constitute the additional layer of a stack according to the invention, type P, respectively N. The second coating, and where appropriate, the third coating may define the N-type or P-type intermediate layer of the stack according to the invention.

The method comprises a step d), subsequent to step c), of depositing a second active layer, for example different from the first active layer, on the second coating formed in step b) or, if appropriate, on the third coating formed in step c). Those skilled in the art then know how to determine the deposition conditions and the constituents of the solutions to be deposited so as to form a useful stack for a multi-function photovoltaic cell, and in particular of the tandem type according to the invention.

PHOTOVOLTAIC CELL

An organic photovoltaic cell of the multijunction type and in particular of the tandem type according to the invention comprises a stack according to the invention or obtained by means of a method according to the invention.

In particular, as illustrated in FIGS. 4 to 4, it may comprise a succession of superimposed layers joined to each other, in the following order: a support 8, which is preferably in the form of a plate, for example made of glass or plastic, preferably of PEN and / or PET,

a first electrode 1 1, or lower electrode,

an assembly formed in all or part of a multilayer stack according to the invention as described above, and

a second electrode 29, or upper electrode.

The photovoltaic cell preferably comprises electrical connection means (not shown in FIG. 1), in particular contact pickups, which make it possible to connect the electrodes to supply current to an electrical circuit.

The first electrode, in contact with the support, is for example formed of a layer made of a material chosen from indium-doped tin oxide (ITO), aluminum-doped zinc oxide (AZO) , gallium doped zinc oxide (GZO), indium doped zinc oxide (IZO) and mixtures thereof, or formed of a AZO / Ag / AZO multilayer assembly. It may also consist of a network of metal nanowires as described above, preferably consisting of silver nanowires.

The second electrode is preferably formed by a silver layer, or by a network of nanowires, preferably silver.

In one embodiment, the photovoltaic cell may comprise a stack according to the first embodiment, that is to say having an interposed intermediate layer and in contact with the first and second active layers.

It may then be such that the intermediate layer of the stack constitutes a central electrode 70, as illustrated in FIGS. 1 and 2. The first central electrode may be connected to the second electrode by a conventional method known to the person skilled in the art. job. The first and second electrodes may be connected to the central electrode via an electrical circuit. The organic photovoltaic cell and tandem type can thus be of the "3-wire" type.

Alternatively, the photovoltaic cell according to the invention may comprise a stack according to the second embodiment, that is to say having an additional layer 41 interposed between the intermediate layer 20 on the one hand and the first active layer 17 or the second active layer 23 on the other hand. It can then be a "2-wire" type cell. Preferably, the network of nanowires 22, the intermediate layer 20 and the additional layer 41 of the stack form a multilayer recombination element 45 promoting the recombination of the charge carriers within the stack. EXAMPLES

The following nonlimiting examples are presented for the purpose of illustrating the invention.

Example 1

The manufacture of the photovoltaic cell of Example 1 is carried out by following the successive steps described below.

i) A carrier made of ethylene polynaphthalate (PE) is previously prepared for the deposition of layers. Repetitions of chromium / gold contact are deposited on the support, then the support is defatted and treated with oxygen plasma.

ii) A first electrode is formed on the support by depositing on one side of the support, by ultrasonic spray, a solution of silver nanowires diluted in methanol at a content of 0.5 grams per liter of methanol. This deposit is made by performing several successive scans on the face of the support to form a network of silver nanowires on the surface of the support having an electrical surface resistivity greater than 10 Ω / sq and less than 50 Ω / sq. The network of nanowires is then compressed using a press at a temperature of 80 ° C for 30 minutes. After this treatment, the surface resistivity and the transmittance are measured and are respectively less than 25 Ω / sq and approximately equal to 90%.

iii) A first N-type coating of ZnO is then deposited on the first electrode. For this, a solution is prepared, comprising 6% ZnO, as a weight percentage on the mass of the solution, the rest being ethanol. It is spinned for 30 seconds, the speed of rotation of the spinning being set at 1000 revolutions / minute. Repeats of contact are then washed with a cotton swab impregnated with isopropanol (EPA). The multilayer structure obtained by these first layer deposits is then annealed for 5 minutes at a temperature of 140 ° C.

(iv) A mixture consisting of 93% by volume of orthodichlorobenzene

(oCDB) and 7% methyl naphthalene is then prepared as the solvent. In this solvent are added 38 grams per liter of solvent Poly (3 ~ hexylthiphene) (P3HT) and [6,6] -phenyl-C61-methyl butanoate (PCBM), the mass to mass ratio of PCBM being 1 / 0.88, so as to form a solution for the deposition of a first active layer. This solution is then deposited on the multilayer structure, the turntable rotating at a speed of 1500 revolutions per minute for 40 seconds, so as to form a first active layer on the first ZnO coating previously formed. The contact recoveries are then washed with oCDB, then the multilayer structure now comprising the first active layer is annealed for 10 minutes at a temperature of 120 ° C.

v) A first mixture coating of PEDOT and PSS (also called PEDOT: PSS), is then formed on the multilayer structure formed in the previous step, by spraying with a PEDOT solution: PSS of trade name Heraeus HTL Solar, first at a speed of 1500 revolutions per minute for 25 seconds, then at a speed of 3000 revolutions per minute for 25 seconds. Repeats of contact are then washed with isopropanol or deionized water. The susbtrate is then annealed at a temperature of 120 ° C for 10 minutes in a glove box.

vi) A network of silver nanowires is formed on the PEDOT: PSS coating in a manner identical to that detailed in step i).

vii) A second coating of PEDOT: PSS is formed on the network of nanowires formed in step vi) according to the method described in step v).

viii) A second active layer is formed on the second layer of

PEDOT: PSS following a method identical in all respects to that described in step iv).

Thus, the first coating of PEDOT: PSS, the network of nanowires formed in step vi) and the second coating of PEDOT: PSS together define a central electrode in the form of an intermediate layer in contact with the first and second active layers .

ix) A second N-type ZnO coating is then formed on the second active layer under conditions identical to those described in step iii), the speed of rotation of the spool being set at 2000 revolutions per minute.

x) Finally, a second silver electrode with a thickness of 100 nm is formed on the multilayer structure obtained in step ix) by evaporation under vacuum.

In this way, a NIPIN type assembly is obtained as illustrated, for example, in FIG. 7. A 3-wire tandem type organic photovoltaic cell comprising the assembly obtained using steps i) to x) described above has an average yield of 3%, which is 0.5 percentage points higher than the efficiency of a conventional tandem organic photovoltaic cell having a central electrode consisting of a silver film deposited by vacuum evaporation.

Example 2

Example 2 differs in particular from Example 1 in that the support is made of glass and the lower electrode is indium tin oxide (ITO).

The assembly is obtained by following steps i) to x) of Example 1. H has an average yield of 3%, 0.5 points higher than the yield of a conventional tandem cell having a central electrode consisting of a silver film deposited by evaporation under vacuum. Example 3

The preparation of Example 3 differs from Example 1 only in that steps vii and ix) are inverted so as to form steps ix ') and vii') respectively, the rotation speed at step vii ') being nevertheless set at 1000 revolutions per minute.

Thus, the first coating of PEDOT: PSS and the network of nanowires formed in step vi) form an intermediate layer, the second coating of ZnO formed in step vii ') constitutes an additional layer. These intermediate and additional layers together form a multilayer charge carrier recombination element.

In this way, a PIN / PIN connection is obtained. A 2-wire tandem type organic photovoltaic cell incorporating the stack of Example 3, as shown schematically in FIG. 5, has an average yield of 3%, which is 0.5 percentage points higher than the efficiency of a cell. conventional tandem type organic photovoltaic device having a charge carrier recombination layer consisting of a silver film deposited by vacuum evaporation. The invention is obviously not limited to the embodiments described and shown.

Claims

A multilayer stack (5) useful for forming an organic photovoltaic and multijunction cell (32), said stack comprising first (17) and second (23) active layers, and a P-type intermediate layer (20) or N-type, interposed between said first and second active layers and in contact with at least one of the first and second layers, said intermediate layer integrating an array (22) of electrically conductive nanowires, the multilayer stack comprising an additional layer (41) interposed between the first active layer and the second active layer and directly in contact with the first active layer or the second active layer, the additional layer being of a P or N type, distinct from that forming the intermediate layer.

2. Stack according to the preceding claim, the network of nanowires extending parallel to the intermediate layer.

3. Stack according to any one of the preceding claims, the network of nanowires being devoid of contact with said first and second active layers.

4. Stack according to any one of the preceding claims, the thickness of the intermediate layer being greater than or equal to 100 nm and less than or equal to 500 nm.

5. Stack according to any one of the preceding claims, the network of nanowires being at least partially in contact with the additional layer.

6. Stack according to any one of the preceding claims, the nanowire array extending at the interface between the intermediate layer and the additional layer.

7. Stack according to any one of the preceding claims, the nanowire array being non-percolating.

8. Stack according to any one of the preceding claims, wherein the assembly consisting of the intermediate layer and the additional layer has a thickness greater than or equal to 100 nm and less than or equal to 500 nm.

9. Stack according to any one of the preceding claims, the transmittance of the assembly consisting of the intermediate layer and the additional layer being greater than 50%.

10. Stack according to any one of the preceding claims, the surface resistivity of the assembly consisting of the intermediate layer and the additional layer being less than 200 Ω / sq, preferably less than 100 Ω / sq.

11. Stack according to any one of the preceding claims, the nanowires being metallic, preferably made of a metal selected from silver, copper, gold and their alloys.

12. Stack according to any one of the preceding claims, the nanowires having an average diameter greater than or equal to 10 nm, preferably greater than or equal to 20 nm, and less than or equal to 1000 nm, preferably less than or equal to 150 nm. , and an average length greater than or equal to 1 μιη and less than or equal to 500 μηι, preferably less than or equal to 30 μπι.

13. Stack according to any one of the preceding claims, the material of the intermediate layer and / or of the additional layer being chosen from the group formed by

P-type polymers and P-type oxides, in particular the mixture of poly (3,4-ethylenedioxythiophene) (PEDOT) and sodium polystyrene sulfonate (PSS), Nafion, WO ₃ , MoO ₃ , V ₂ 0 ₅ and NiO and mixtures thereof,

or

N-type polymers and N-type oxides, in particular ethoxylated polyethylenimine (PEIE), poly [(9,9-bis (3 '- (N, N-dimethylamino) propyl) -2,7-fluorene ) -alt-2,7- (9,9-dioctylfluorene) (PFN), ZnO, titanium oxides TiO _x with x ranging from 1 to 2, zinc oxide doped with aluminum (AZO), indium-doped zinc oxide (IZO), gallium-doped zinc oxide (GZO), and mixtures thereof.

A method of manufacturing a stack, comprising at least the steps of:

a) having a first active layer in contact with a first coating

(63) P-type or N-type,

b) depositing on said first coating a first solution comprising nanowires and optionally a P type or N type material, under conditions conducive to the formation, on the surface of said first coating, of a second coating;

(64) integrating a network (22) of nanowires, c) optionally, depositing on the second coating formed in step b) a second solution comprising a P-type or N-type material, different from that of the first solution, under conditions conducive to the formation of a third coating (66)

the first coating constituting the additional layer on the one hand, and the second coating, and optionally the third coating, constituting the intermediate layer on the other hand, a stack according to any one of the preceding claims.

15. Method according to the preceding claim, comprising a step d), subsequent to step c), of forming a second active layer on the second coating formed in step b) or on the third coating formed in step vs).

16. Multijunction type organic photovoltaic cell, and in particular of the tandem type (32), comprising a stack according to any one of claims 1 to 13 or obtained by means of a method according to any one of claims 14 and 14. 15.

17. Photovoltaic cell according to the preceding claim, wherein the network of nanowires, the intermediate layer and the additional layer of the stack forms a multilayer charge carrier recombination element (45).